1. Field of the Invention
The present invention relates to assemblies for mounting antennas to poles.
2. Description of Related Art
The present invention is particularly intended for use on directional antennas, although it may be used for omni-directional antennas as well. A directional antenna is an antenna with a gain that is sensitive to its angular orientation. The angular orientation is commonly measured in terms of azimuth (i.e. "horizontal angle") in combination with an elevation (i.e. "vertical") angle. An assembly for mounting such an antenna is preferably provided with a bracket that includes a clamp for mounting to the pole and a support structure for supporting the antenna relative to the clamp. The bracket typically also has components for adjusting each of the azimuth and the elevation angle, so that the gain can be maximized. The support structure is attached fixedly to the clamp, and azimuth and elevation angle of the antenna plate are adjusted with respect to the support structure.
Adjustment of the azimuth is obtained conventionally by orienting the bracket around the vertical pole properly. A separate component might not be provided for adjusting the azimuth. For example, the bracket illustrated in U.S. Pat. No. Des. 361,068, provides for only elevation angle adjustment.
The adjustability of the orientation of the clamp around the pole may not provide a high enough resolution in azimuth, especially for heavy or highly directional antennas that permit only a small error in angular orientation. Indeed, some microwave antennas weigh over 50 lbs. To be installed, the assembly must be lifted up to the desired point on the pole and then, with the associated transceiver operating, rotated horizontally around the pole until the maximum gain is registered. That procedure determines the exact orientation for clamping, which must be maintained continuously during attachment of the clamp to the pole.
Given such difficulties, many bracket assemblies are provided with an additional component for azimuth adjustment. FIG. 1 shows a representative conventional bracket providing such azimuth adjustment. A directional antenna transceiver 40 is mounted on a pole 42 by a bracket assembly 44 supporting an antenna base 46, to which the transceiver is attached. Bracket assembly 44 has a clamp 48 and a support structure 50 that is attached to the clamp. The bracket assembly is further provided with an azimuth adjusting screw 52, which couples the base to the support structure. The adjusting screw rotates the antenna around pivot point 54 along the direction indicated by the arrow 56. An elevation adjustment component, not shown in the plan view of FIG. 1 is also included in the bracket.
A problem with such brackets is that large mechanical stresses or loads become highly concentrated on very few components. Pivot point 54 is subjected to large loads because of the weight of the antenna and strong wind forces. Moreover, screws that adjust the azimuth angle are subjected to the wind forces, while screws that adjust the elevation angle are subjected to the weight of the antenna.
What aggravates this problem is the competing design requirements of the azimuth and elevation angle adjusting screws. Such screws should have fine threads to provide a high resolution for tuning the antenna angle they control. Simultaneously, they should be robust enough to withstand large forces applied to them, without losing the set adjustment.
Another source of problems is that the adjustment components are exposed. These components are thus subject to deterioration due to the weather, vulnerable to vandalism, and unsightly (which can be a problem in code stringent areas).